Process for installing an offshore tower

ABSTRACT

Process for installing an offshore tower, specifically a substructure, which basically comprises the following steps: a) dry manufacturing a foundation comprising a block ( 1, 1 ′) basically made of concrete and dry manufacturing a base section ( 25 ) of a shaft ( 2 ); b) applying said base section to said foundation block, forming a unit called the “starting unit”; c) moving said starting unit to the installation point of said substructure; and d) actuating in a controlled manner, first ballast valve means in such a manner that said starting unit sinks until resting on the seabed; having placed said foundation block or said starting unit in the body of water where the installation point said substructure is located.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. national phase of International Patent Application No.PCT/EP2011/066462, filed on Sep. 21, 2011. Priority under 35 U.S.C. §119(a) and U.S.C. § 365(b) is claimed from Spanish Patent ApplicationNo. P201001212, filed on Sep. 22, 2010, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a process for installing a towerbasically made of concrete, for use in a body of water, mainly at sea(therefore normally referred to as “offshore”).

In particular, the present invention relates to a process for installinga tower shaft basically made of concrete, of the semi-submerged (orsemi-emerged) type in installed condition, and a corresponding towerfoundation also basically made of concrete, of the submerged type ininstalled condition.

This type of assembly is mainly used as a support for wind turbines andin said case is globally referred to as “substructure.” Throughout thisspecification, for the sake of simplicity, the term substructure shallbe used to refer to the unit formed by the shaft and foundation, withoutlimiting the scope of the description or claims to the application ofthe object of the invention to wind turbines.

This invention is applicable both to substructures basically made ofconcrete in their entirety and to substructures having a foundationbasically made of concrete and a shaft mainly made of concrete up to acertain height above the water level and mainly of another material (forexample, steel), above said certain height.

Therefore, the main sector of application of the invention is therenewable or green energy industry, particularly wind energy.

BACKGROUND OF THE INVENTION

The growing importance of wind energy in recent years in Spain, Europeand the rest of the world is well known, and forecasts point tosustained growth in the generation of wind energy worldwide. The energypolicies of the most advanced and economically powerful countriesinclude an increased presence of wind energy among their objectives.

Within this context, offshore wind farms are starting to appear, thusconfirming the forecasts of sharp growth in the application of thistechnology in forthcoming years. While wind farms built on offshoresites are undoubtedly more expensive, logically depending on the depthof the waters where they are installed, the wind has greater quality,higher speed and less turbulence and, consequently, the number ofproduction hours is higher which, added to the greater air density atwater level, generates greater revenues than land-based farms,compensating the cost overrun of the initial investment.

The development and construction of offshore wind farms is frequent andthe number of marine wind farms currently under study has grownsignificantly, particularly in Germany, the British Isles andScandinavian countries, consistent with the predicted growth of thesetypes of farms, closely linked to the strategic objectives establishedat state level aimed at reaching certain renewable energy quotas. Thetendency to use higher-powered and larger wind turbines with theobjective of reducing the unit cost of installed power has beenever-present in wind turbine development and is, if possible, even moreaccentuated in the case of offshore wind energy. Practically all largewind turbine manufacturers have high-power models, three-megawatt ormore, under study or in advanced stage of development, adapted to seaconditions, which are particularly demanding. This, in turn, representsa significant increase in substructure-related specifications andrequirements—foundation and shaft—imposed on the wind turbines which,added to their use in increasingly deep sites, will require thedevelopment of novel concepts for said substructure, with increasedcapacity and competitive cost.

The solutions generally envisaged in the current state of the art forthe construction of offshore farms are listed and described below in anorientative and non-limiting manner.

Shallow water depths:

-   -   Driven metal monopile not connected to the tubular metal tower        shaft itself.    -   Gravity-based foundations: structural concrete footing, often        with pedestals. These are transported and anchored using barges        and/or sea cranes.    -   Suction bucket: based on driving watertight buckets into the        seabed and consequently leveraging the differences in pressure        generated.

Medium and deep water depths:

-   -   Tripod: The metal tower is supported by a structure having three        tilted legs that rest on the seabed by means of driven piles or        other similar system. The tower may be centered in relation to        the tripod legs or disposed on one of said legs.    -   Tripile: The metal tower rests, by means of a cross-shaped        transition part having three arms, on three vertical piles        submerged and driven into the seabed.    -   Jacket: The metal tower is supported by a jacket structure        having four legs or columns.

In the case of ultra-deep water depths, floating solutions anchored tothe seabed have been envisaged.

An overview of the state of the art results in the following generalconsiderations:

-   -   All solutions are based on shafts in the case of metal        tubular-type towers.    -   Solutions for medium and deep water depths include a change in        tower shaft typology, with a metal tubular tower for the emerged        part and a highly differentiated element for the submerged part        (tripod, jacket, etc.).    -   Concrete gravity-based foundations are envisaged for shallow        depths, such as semi-submerged structures, and include        installation by means of sea cranes.

Among the main drawbacks and limitations of the known solutionsenvisaged for the substructure of an offshore wind turbine, thefollowing must be highlighted:

-   -   High costs deriving from the scarce and expensive means for        transporting, handling and lifting the foundation, tower and        turbine elements at sea.    -   Low durability of steel in marine environments due to the        aggressive environmental conditions (high humidity/salinity),        particularly in tidal zones, entailing high and expensive        maintenance requirements. This, added to the high sensitivity of        metal structures to fatigue loads, limits the useful life of the        metal components of the substructure.    -   Highly sensitive to collisions with sea vessels, icebergs and        drifting objects in general.    -   Highly dependent on complex and uncertain geotechnics in the        different cases of gravity-based foundations.    -   In cases of ultra-deep water depths: complex, delicate and        expensive transition zones between the emerged tubular shaft of        the tower and the different types of partially submerged        elements connected to the foundations at seabed level.    -   High environmental impact of driven pile solutions due to the        noise and vibrations generated by these during execution        thereof.    -   Uncertainties deriving from variability in steel pricing,        notably more accentuated than that of concrete.    -   High sensitivity to critical connection details with foundations        by means of driven piles, which must support the low redesign        accuracy of driven solutions and have been a source of        significant pathologies in current farms.    -   Metal tubular towers are based on factory-made,        closed-circumference tube parts which limits maximum diameters        if road transport is required. This limits tower capacity and        height. If larger diameters than those transportable by road are        sought by manufacturing the towers in shipyards or coastal        facilities, this will considerably limit the potential        industries and factories for manufacturing these towers.    -   Solutions involving limited tower shaft rigidity, which limits        capacity for greater tower heights and wind generator sizes,        particularly with low-rigidity foundation solutions, which is        the most frequent case in offshore installations.    -   Expensive elements for the submerged part of the installation,        increasing exponentially with depth.    -   High dependence on specific means for lifting and transport in        marine environments, which are very limited in range.

SUMMARY OF THE INVENTION

The present invention aims to resolve or mitigate the drawbacks andlimitations of the prior art.

Structural concrete has been proven to be a suitable material foroffshore constructions, particularly marine constructions.

Thereby, the present invention promotes the use of structural concretefor the tower as a technically and economically advantageous material indifferent aspects, particularly for applications in the demanding andaggressive marine environment. Although metal structures are mainly usedin mobile floating elements, as an extension of naval practices andalways associated with uninterrupted maintenance, concrete is in turn anadvantageous alternative and therefore more frequent in all kinds ofpermanent-type marine constructions (ports, docks, wharves, breakwaters,rigs, lighthouses, etc.).

This is basically due to the structural durability, robustness andresistance to the low sensitivity to marine corrosion and to thepractically maintenance-free service life of structural concrete.Adequately designed, its useful life normally exceeds fifty years.

Additionally, concrete offers advantages due to its tolerance to impactsor collisions and can be designed, for example, to support the forcesgenerated by drifting ice or the impact of small ships, as well as theease and economy of eventual repair thereof.

Structural concrete is also a universal construction material and theraw materials and means for manufacturing it are readily availableworldwide and relatively inexpensive.

It is therefore known and accepted that concrete is an especiallyadequate material for marine construction and the present inventionpromotes use thereof, allowing leveraging of its qualities for theparticular restraints and circumstances of offshore wind farms, asopposed to current practices for the construction of these types offacilities, which are based on the use of steel.

Specifically, the present invention relates to a process for installinga substructure which includes: a tower shaft basically made of concrete,of the semi-submerged type in installed condition, and a correspondingtower foundation also made of concrete, of the submerged type ininstalled condition.

Said shaft is formed of at least two cylindrical sections basically madeof concrete, in most cases tapered upwards in installed condition, whichare placed one on top of the other coaxially until completing theenvisaged height. Therefore, there are respective horizontal jointsbetween the successive sections. One section of the shaft is intended tobe disposed in installed condition directly over said foundation andshall hereinafter be referred to as the “base section” (any sectionapart from the base section shall hereinafter be referred to as the“superposition section”).

Each of said sections can be made from a single piece (hereinafterreferred to as “integral section”). Alternatively, at least one of saidsections can be formed of at least two circular arc parts (orvoussoirs), disposed side-by-side until completing the envisagedcircumference of the corresponding section. Therefore, there arerespective vertical joints between successive voussoirs.

The installation process according to the present invention comprisesthe following steps, in chronological order:

a) dry manufacturing a foundation comprising a block basically made ofconcrete, said foundation block being essentially hollow and watertightand having ballast valve means for opening a passage to the interior ofsaid foundation block, and dry manufacturing a base section of a shaftand dry manufacturing the superposition section(s) of a shaft

b) applying, mechanically or integrally, said base section to saidfoundation block in such a manner that said base section and saidfoundation block assume the relative position envisaged for theinstalled condition, said base section and said foundation block forminga unit hereinafter referred to as “starting unit”;

c) moving said starting unit, in a self-floating manner, through thebody of water wherein the installation point of said substructure islocated, up to the installation point of said substructure; and

d) actuating, in a controlled manner, said first ballast valve means ofsaid foundation block so as to open a passage to the interior of saidfoundation block and introduce ballast in said foundation block throughsaid passage in such a manner that said starting unit sinks untilresting on the bottom of the body of water.

The installation process according to the present invention alsocomprises the following step:

after step a) and before step c): e) placing said foundation block orstarting unit in the body of water wherein the installation point ofsaid substructure is located.

For example, said foundation block and said base section are drymanufactured using dry docks and sluices, in order to allow floatationof the foundation block and the base section from the same point ofmanufacture thereof, or using ramps such as those used to launch largeships and other marine structures.

The installation process according to the present invention can alsocomprise the following step:

after step e): f) dispose said foundation block in a position such thatsaid ballast valve means are submerged at least partially in the body ofwater where the installation point of said substructure is located.

If the installation process according to the present invention includesstep f), the ballast that is introduced in step d) can be water from thebody of water where the installation point of said substructure islocated.

In the installation process according to the present invention, saidfoundation block is configured in such a manner as to have thefloatability required for step c). Additionally or alternatively, saidstarting unit is configured in such a manner as to have the floatabilityrequired for step c). In addition, the installation process alsocomprises the temporary use of auxiliary floating structures to increasethe stability of the floating whole. Therefore also comprising, afterstep a), the following step:

g) laterally applying at least one auxiliary structure having positivefloatability to said foundation block and/or to said base section insuch a way that said auxiliary structure is never fully submerged duringthe installation process.

the installation process according to the present invention alsocomprises the following step:

after step a) and before step c): h) applying at least part of saidsuperposition sections to said foundation block and/or to said basesection and/or to said auxiliary substructure.

It should be understood that, in the event that one of saidsuperposition sections is formed from voussoirs, the dry manufacturingsaid superposition sections includes the pre-assembly of said voussoirsuntil forming complete sections.

At least one said superposition sections are applied in step h) to saidfoundation block and/or to said base section and/or to said auxiliarystructure in a temporary position, i.e. in a position different to theposition they occupy in installed condition. Thereby, the installationprocess according to the present invention also comprises the followingstep:

after step h) and step c) i) disposing said superposition sections ofsaid starting unit in such a manner that said superposition sectionsassume the position envisaged for the installed conditions in relationto the starting unit.

The installation process according to the present invention can alsocomprise the following step:

after step a) and before step c): j) applying wind turbine means to saidfoundation block and/or to said base section and/or to saidsuperposition sections and/or to said auxiliary structure.

Preferably, said wind turbine means are applied in step j) to saidfoundation block and/or to said base block and/or to said superpositionsections and/or to said auxiliary structure in a temporary position,i.e. in a position different to the position it occupies in installedcondition, in which case the installation process according to thepresent invention also comprises the following step:

after step j): k) disposing said wind turbine means in such a manner asto assume the position envisaged for the installed condition.

The installation process according to the present invention can alsocomprise the following step:

after step a) and before step i): l) applying lifting means for towerassembly to said foundation block and/or said base section and/or saidauxiliary structure.

Optionally, said foundation block is multicellular (i.e. it isinternally divided into watertight enclosures by means of partitionwalls). In this case, at least one of said partition walls can includefirst distribution valve means for fluid communication between adjacentwatertight enclosures, in which case said first distribution valve meanscan be actuated in such a manner as to cause spatially selectiveballasting of said foundation block, in order to aid the orientation ofsaid starting unit during transport or sinking or anchoring.

Additionally, said foundation block can be platform-shaped, preferablywith a box-shaped configuration with a quadrangular or circular base.

Said ballast valve means and said distribution valve means can includeremote actuation means and/or predetermined automated actuation means.

Said ballast valve means and said distribution valve means can beactuated in a controlled manner before step d), in such a manner as topartially ballast said starting unit in order to position and/or givegreater stability to said starting unit at any time prior to sinking andanchoring thereof.

It must be pointed out that, by means of a special type of towerintended for enabling high-capacity wind turbine support towersolutions, the present invention provides a repowerable substructure.That is, a substructure originally designed with increased capacity andadaptability for allowing repowering (the future substitution of anoriginal wind turbine for another with greater output power, efficiencyand profitability) leveraging the same substructure. A repowerablesubstructure such as that proposed and enabled by the present inventiongains in meaning and interest to offshore installations for severalreasons, among which the following must be highlighted:

-   -   In the case of offshore farms, the fraction of investment        destined to the infrastructure and civil works increases        qualitatively, due to which the search for concepts which, based        on future repowering, extend the useful life thereof and        facilitate amortisation gains in meaning. The same applies to        the amortisation of the decommissioning costs of the entire        substructure upon concluding its useful life.    -   At present and, in general, substitution of the wind turbine for        onshore repowering also implies substitution of the entire        substructure which, on being a smaller fraction of the total        cost, has a limited influence on the profitability of said        repowering; in the case of offshore, in turn, the investment        destined to the substructure represents a much larger fraction        of the total and the complete substitution would significantly        penalise the profitability of a possible repowering.    -   Wind turbines having greater output power and rotor diameter        require a larger distance between positions in order to prevent        the presence of the turbine from affecting wind conditions in        neighbouring turbines. Initially planning repowering of the        substructure itself would therefore imply initially envisaging        certain inter-distances between wind turbines larger than those        strictly necessary in a first phase. This represents a drawback        in onshore farms due to the greater occupation of land which,        however, decreases significantly in the case of offshore farms.    -   In onshore farms, the substructure loads and requirements that        govern its design and cost are nearly exclusively due to the        wind turbine. In offshore towers, in turn, a very large part of        the tower and foundation requirements are due to the action of        the waves and currents which are independent of the wind        turbine. Consequently, an increase in the size of the wind        turbine implies a relative increase in total substructure loads        far below the equivalent in the case of onshore farms,        particularly in the case of ultra-deep sites. This significantly        limits the initial overrun cost of preparing the substructure of        an offshore turbine so that it can support larger turbines in        the future.    -   In offshore farms, wind shear is much less, which significantly        reduces the necessary height of the tower (above sea level) for        a certain rotor diameter. This facilitates the possibility of        maintaining the same tower for a future wind turbine having        greater output power and rotor diameter.    -   A repowerable substructure allows full leveraging of the        improved durability of concrete structures in marine        environments, as well as their lower fatigue sensitivity,        thereby preventing their useful life from being unnecessarily        limited by the less durable elements, which are the wind turbine        and its different components.    -   Wind turbines built for offshore application are considerably        more expensive, regardless of their substructure, due to the        much more stringent requirements in terms of durability in        marine environments throughout their useful life, generally        established at twenty years. Initially envisaging shorter-term        repowering can allow a reduction in requirements in this regard        for the first wind turbine, which could be designed for a        shorter useful life, with the ensuing reduction in cost.    -   In general, and finally, experience in the development and        evolution of wind turbine technology has shown that the period        of practical obsolescence of turbine energy generation capacity        in relation to the latest developments and the state of the art        can be much shorter than the useful life of the generator        itself, generally established at twenty years. Predicting a        similar trend in the emerging offshore wind energy sector, and        therefore that profitability can be improved by incorporating        more efficient future technology (repowering) in a period of        less than twenty years makes technological and economic sense.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further characteristics and advantages of the invention willbecome evident from the following description of an embodiment of theinvention, provided solely by way of non-limiting example, withreference to the accompanying drawings, wherein:

FIG. 1 shows a schematic front view of an embodiment of an offshoretower which can be assembled following the installation processaccording to the present invention;

FIG. 2 shows a schematic top plan view of a first starting unit which isbeing towed with superposition sections thereupon;

FIG. 3 shows a schematic sectional top plan view of the internalconfiguration of the foundation block of the starting unit of FIG. 2;

FIG. 4 shows a schematic sectional front view of the starting unit ofFIG. 2 with superposition sections thereupon;

FIG. 5 shows a schematic sectional front view corresponding to FIG. 3but at a later stage of the installation, according to the presentinvention;

FIG. 6 shows a schematic front view of a detail of the assembly of FIGS.2 to 5, in partial cross-section;

FIG. 7 shows a schematic top plan view of a second starting unit withtwo auxiliary floatability structures which support superpositionsections and wind turbine means;

FIG. 8 shows a schematic sectional top plan view of the internalconfiguration of the foundation block of the starting unit of FIG. 7;

FIG. 9 shows a schematic sectional front view of the starting unit ofFIG. 7 with two auxiliary floatability structures which supportsuperposition sections and wind turbine means;

FIG. 10 shows a schematic sectional front view corresponding to FIG. 8but at a later stage of an installation process according to the presentinvention with the auxiliary flotability structure which remains atleast partially emerged during the installation process;

FIG. 11 shows a schematic elevational view and top plan view, both incross-section, of a detail of the assembly of FIGS. 7 to 10,specifically the configuration of superposition sections supported by anauxiliary floatability structure of the assembly of FIGS. 7 to 10,configuration wherein said superposition sections are essentiallydisposed on the same axis and level, with the smaller sections insidethe larger sections, hereinafter referred to as “multi-layeredconfiguration”;

FIG. 12 shows a schematic top plan view of an assembly of starting unitshaving common auxiliary floatability structures;

FIG. 13 shows a schematic front view of a third starting unit which isbeing towed, with superposition sections and means for assembling towersthereupon;

FIG. 14 shows a schematic front view corresponding to FIG. 13 but at alater stage of the installation process according to the presentinvention;

FIG. 15 shows a schematic plan view and front view of a starting unit inthe floated transportation phase, with connected auxiliary floatingstructures and superposition sections and wind turbine means beingtransported over the foundation block and the auxiliary floatingstructures;

FIG. 16 shows a schematic plan view and front view of the group showedin FIG. 15 during the ballasting process.

DETAILED DESCRIPTION OF THE INVENTION

Initially referring to FIG. 1, an embodiment of an offshore wind tower27 is shown, that is, a substructure 1, 1′, 2 for supporting windturbine means 16, susceptible of being installed by means of theinstallation process according to the present invention.

Said tower 27 is formed by a foundation block, specifically a submergedplatform 1, 1′ acting as a gravity-based foundations, basically made ofstructural concrete, full of ballast, and a shaft 2, of thesemi-submerged type, which in turn includes a plurality of sections 25,7 mainly formed by concrete voussoirs 3, also including horizontaljoints 4 and vertical joints 5 between said sections 25, 7 and saidvoussoirs 3, respectively. Said substructure 1, 1′, 2 supports windturbine means 16. For certain applications, not according to theinvention, said substructure can comprise only the platform 1, 1′ andbase section 25, disposing said wind turbine means 16 directly on saidbase section 25.

Said platform 1, 1′ is dry manufactured (on land, dry docks, coastal orfloating ports, or other enabled and protected coastal or maritimefacilities) and configured following the installation process of thepresent invention in such a manner that, during installation phasesprior to shaft 2 assembly, said platform 1, 1′, without ballast,provides a provisional and stable floating platform which enablestransport by self-floatation with the corresponding base section 25applied thereto (said foundation platform and said base section thusforming a starting unit 1, 1′, 25), to its final site.

Therefore, according to the installation process according to thepresent invention, the voussoirs 3 that form at least some sections 25,7 of the shaft 2 are assembled prior to transport thereof in open sea,in such a manner as to transport sections 25, 7 already pre-assembledand complete.

The final assembly of the shaft 2 by successive stacking of thesuperposition sections 7 is generally carried out at the final site.

Platform 1, 1′ is substantially flat and horizontal and built ofstructural concrete, whether using in-situ concrete techniques or byassembling prefabricated parts or panels, or a combination of both. Theplan and elevation geometry thereof may vary in accordance with specificproject requirements, adopting for example significantly circumferential1 floor plan configurations, whether with a curved or polygonalperimeter, or quadrangular 1′ type configurations aimed at simplifyingconstruction thereof, as well as other regular or irregular polygonshapes. The dimensions of the platform 1, 1′ are predetermined inaccordance with known techniques in such a manner that:

-   -   wind tower 27 stability in installed condition is provided,        thanks to its own weight and that of the ballast, and to        adequate load transfer on the seabed,    -   a platform 1, 1′ is provided, having the floatability and        stability required for said previous function as a provisional        floating and stable platform,    -   a starting unit 1, 1′, 25 is provided, having the necessary        space and resistance to transport superposition sections 7 or        other necessary components and equipment.

The flat morphology and large volume of the foundation platform 1, 1′allow limitation of the necessary water depths for floatation thereof,thereby reducing the operating requirements for the infrastructures thatserve for manufacturing and subsequent floating thereof.

FIGS. 2 to 6 relate to a first example of an offshore tower for theinstallation process according to the present invention.

Specifically, FIG. 2 shows a starting unit 1, 25 which is being towed ina self-floating manner along the sea surface prior to sinking thereof,with superposition sections 7 disposed thereupon.

FIG. 3 shows the platform 1 of FIG. 1, configured by way of amulticellular circular box, which comprises a lower slab 11, an upperslab 12 and a peripheral slab 9, as well as a plurality of straight,rigid inner ribs 10. The ribs 10 are disposed forming squares whichdelimit inner enclosures 13. For example, the lower slab 11 andperipheral slab 9 are executed by means of in-situ concrete, and theupper slab 12 and ribs are materialised by means of prefabricatedalveolar slabs. The platform 1 comprises a circumferential rib 26 whichcoincides with the circumferential extension of the base section 25 andis structurally prepared for mechanically connecting to the base section25 by means of the upper slab 12.

At least one of the lower 11, upper 12 or peripheral 9 slabs has ballastvalves, and at least part of said inner enclosures 13 are watertightand/or have distribution valves. These inner enclosures provide anadequate floatation volume for said function as a provisional and stablefloating platform; additionally, upon reaching the installation point,controlled filling, totally or partially, with ballast (for examplewater 17) of all or some of these enclosures 13 by means of said ballastvalves and/or said distribution valves helps to carry out the sinkingoperation of the starting unit, in such a manner as to correctly orientsaid starting unit.

Remote actuation means and/or predetermined automated actuation meanscan be incorporated to actuate said ballast valves and/or saiddistribution valves. There can also be intermediate stable phases duringthe sinking operation, wherebetween superposition section 7 assemblyphases are interspersed. To this end, different floatationconfigurations can be used, varying the selective filling of the innerenclosures 13. Finally, said inner enclosures can remain filled withballast 17 in their final situation after installation in order togenerate greater stabilising weight.

As shown in FIGS. 2 and 4-6, at least part of the superposition sections7 can be transported on the starting unit 1, 25, whether in their finalposition on said starting unit 1, 25 or, as shown, in a provisionalposition enabled for transporting the superposition sections 7.

As shown in FIG. 5, the starting unit 1, 25 can use the internal volumeof the platform 1 and also the internal volume of the base section 25 asfloatation volume. In fact, the floatation of said internal volume ofthe base section 25 can complement or substitute the floatation of theplatform 1. The platform 1 can be submerged during transport.

FIG. 5 also shows that securing and anti-collision means can be disposedto aid the sinking of said starting unit 1, 25. Said securing andanti-collision means comprise arms 6 joined in a fixed manner to saidsuperposition sections 7 and in a sliding manner to said base section25, in such a manner that while sinking, the arms 6 move upwards throughthe base section 25 so as to maintain said superposition 7 sectionsconveniently secured to the base section 25, thereby preventing thesuperposition sections 7 (which are floating nearby) from drifting awayand becoming dispersed and/or colliding with the starting unit 1, 25.

Fastening means for provisionally securing the superposition sections 7on said platform 1 may be disposed. As can be particularly seen in FIG.6, in this embodiment said fastening means comprise tensioning cables 8which secure the superposition section 7 to the platform 1 and a base 15whereupon the superposition section 7 rests. Said tensioning cables 8will be released before disposing said superposition sections 7 on saidstarting unit 1, 25 in the position envisaged for the installedcondition. Preferably, said tensioning cables 8 will be released whilesinking the starting unit 1, 25.

In this example of a tower, said superposition sections 7 are adapted bymeans of internal partitioning for self-floatation and, optionally,self-overturning, in such a manner that, when not joined to the startingunit 1, 25 (whether due to being superposition sections 7 which havebeen transported on the starting unit 1, 25, the fastening means ofwhich have become released, or due to being superposition sections 7which have been transported independently to the starting unit 1, 25)these float and can be oriented.

After anchoring, shown in FIG. 5, the superposition sections 7 will beraised and positioned using external assembly means (conventional andtherefore not shown) for executing marine constructions.

FIGS. 7 to 11 relate to a second example of an offshore tower for theprocess of the present invention.

Specifically, in accordance with the project and stability conditionsadopted for the platform 1′, as shown in this example, at least twosections 25, 7 can be stacked in their final position on the platform 1′prior to transporting the assembly by floatation. Likewise, auxiliaryfloating structures 14 can be used, provisional and reusable, whichincrease platform 1′ floatability and stability. These auxiliaryfloating structures 14 are provisionally attached and connected to saidplatform 1′ using adequate anchoring 21 means. These auxiliary floatingstructures 14 also serve, in this example, to transport at least part ofthe superposition sections 7 and wind turbine means 16, with or withoutblades, thereupon. As shown in FIG. 10, this auxiliary flotabilitystructure remains at least partially emerged during the installationprocess.

Guiding means can also be disposed to aid the sinking of said startingunit 1′, 25. As can be particularly seen in FIG. 10, said guiding meanscomprise articulated bars 18 joined in a fixed manner to said auxiliarystructures 14 and in a sliding manner to said base section 25.

As shown particularly in FIG. 11, although also included in FIG. 7, inorder to transport the superposition sections 7 at least part of saidsuperposition sections 7 can be disposed in a temporary multi-layeredconfiguration 22, such that said superposition sections 7 areessentially disposed on the same axis and level, with the smallersections inside the larger sections. This allows greater efficiency ofthe space occupied and can facilitate the assembly operation of thesections, given that it allows successive raising of the superpositionsections without obstacles, whereupon the superposition section havingthe largest diameter and being most outwardly disposed is raised fromits temporary position in each case.

As shown in FIG. 12, assemblies formed by several starting units 1′, 25and auxiliary floating structures 14 common to some of said startingunits 1′, 25 can also be formed for transport operations by floatation.This solution allows a reduction in the number of auxiliary structuresrequired, which can be particularly advantageous if the distance fromthe manufacturing point of said starting unit to the installation pointof the corresponding tower is significantly high.

As now shown in FIGS. 13-14, a crane 20 can be disposed on the platform1, possibly provisional and reusable, for assembling the substructure 1,1′, 7, 25, and optionally the wind turbine means 16 or any of itsconstituent parts. In this case, at least part of the crane 20 mast, forexample the metal jacket, can be transported already installed on theplatform 1 and remain partially submerged after sinking. By way ofexample, as shown specifically in FIG. 14, the crane 20 is secured usingmeans for fastening 19 to sections of the tower itself, and the crane 20parts are provisional and reusable with the exception of asemi-submerged lower part, which is permanent for the purpose offacilitating reinstallation of the crane 20 for maintenance, repair orcomponent replacement operations, etc.

Said crane can be self-mountable, i.e. the tower can be a crane-tower,already known in other applications.

FIG. 15 and FIG. 16 represent another example of an offshore foundationand tower installed following the process of the present invention. Theyrepresent the floating transportation stage and the ballasting stagerespectively. The variations with respect to the example showed in FIGS.7 to 10 are:

-   -   Wind turbine means 16 are also transported in a temporary        position on the auxiliary floating structures 14, together with        the superposition sections 7. Wind turbine means 16 include a        wind turbine nacelle which is transported on top of a        superposition section 7, and a wind turbine blade which is        transported directly over the auxiliary floating structure.    -   The number of auxiliary floating structures 14 is four instead        of two.

Naturally, the principle of the invention remaining the same, theembodiments and construction details can widely vary with regard tothose described and illustrated herein purely by way of non-limitingexample, without departing from the scope of protection of theinvention, as defined in the following claims.

Specifically, by way of illustrative and non-limiting example, while thetower shaft has a circular cross-section in a preferred option ofapplication, alternative polygonal cross-section geometries are alsopossible.

The invention claimed is:
 1. A process for installing an offshore tower,particularly a substructure which includes a tower shaft basically madeof concrete and a corresponding tower foundation basically made ofconcrete, wherein said shaft is semi-submerged in installed conditionsand said foundation is submerged in installed condition; said processcomprising: performing the following steps, in chronological order: (a)dry manufacturing said foundation comprising a block basically made ofconcrete, said foundation block being essentially hollow nd watertightand having a ballast valve means for opening a passage to the interiorof said foundation block, dry manufacturing a base section of said towershaft, and dry manufacturing one or more superposition section(s) ofsaid shaft; (b) applying, mechanically or integrally, said base sectionto said foundation block in such a manner that said base section andsaid foundation block assume the relative position envisaged for theinstalled condition, said base section and said foundation block forminga starting unit; (c) moving said starting unit, in a self-floatingmanner, through the body of water wherein the installation point of saidsubstructure is located up to the installation point of saidsubstructure; (d) actuating, in a controlled manner, said ballast valvemeans of said foundation block so as to open a passage to the interiorof said foundation block for introducing ballast in said foundationblock through said passage, in such a manner that said starting unitsinks until resting on the bottom of the body of water; said processalso comprises, after step (a) and before step (c), step: (e) placingsaid foundation block or said starting unit in the body of water wherethe installation point of said substructure is located; said foundationblock is configured in such a manner as to have the floatabilityrequired for step (c) and/or said starting unit is configured in such amanner as to have the floatability required for step (c); said processalso comprises, after step (a), step: (f) laterally applying to saidfoundation block and/or to said base section at least one positiveauxiliary floating structure which is temporary and reusable, whichremains at least partially emerged during the installation process, andguiding means comprising articulated bars joined in a fixed manner tosaid at least one positive auxiliary floating structure and in a slidingmanner to said base section, wherein both said at least one positiveauxiliary floating structure and said guiding means assist in sinking ofthe said foundation block and/or said base section, such that theguiding means remain emerged during the sinking thereby causing the basesection to sink in, a substantially vertical position until resting onthe bottom of the body of water; said process also comprises after step(a) and before step (c), step: (g) applying at least one of saidsuperposition section(s) to said foundation block and/or to said basesection and/or to said auxiliary structure(s) in a position differentfrom the installed condition in relation to the starting unit; saidprocess also comprises, after step (c), step: (h) disposing saidsuperposition section(s) in said starting unit in such manner that saidsuperposition section(s) assume the position envisaged for the installedcondition in relation to the starting unit.
 2. The process forinstalling an offshore tower according to claim 1, wherein in step (a),the dry manufacturing of said superposition section(s) includes thepre-assembly of long voussoirs having a vertical dimension larger than ahorizontal dimension, until forming complete sections.
 3. The processfor installing an offshore tower, according to claim 1, which alsocomprises, after step (a) and before step (c), step: (j) applying windturbine means to said foundation block and/or to said base sectionand/or to said superposition section(s) and/or to said auxiliarystructure(s).
 4. The process for installing an offshore tower, accordingto claim 3, which also comprises, after step (j), step: (k) disposingsaid wind turbine means in such a manner as to assume the positionenvisaged for the installed condition.
 5. The process for installing anoffshore tower, according to claim 1, which also comprises, after step(a) and before step (h), step: (l) applying lifting means for towerassembly to said foundation block and/or said base section and/or saidauxiliary structure.
 6. The process for installing an offshore tower,according to claim 1, wherein in step (a) said foundation block isinternally divided into watertight enclosures by means of partitionwalls.
 7. The process for installing an offshore tower, according toclaim 6, wherein in step (d) the introduction of ballast in saidfoundation block causes spatially selective ballasting by means ofdistribution valve means for fluid communication with the adjacentwatertight enclosures of said foundation block.
 8. The process forinstalling an offshore tower, according to claim 7, wherein said ballastvalve means and/or said distribution valve means include remoteactuation means and/or predetermined automated actuation means.